Add tuna, chilli, onions, parsley, salt and pepper into a food processor and mix everything together. Make small patties and leave them in the fridge for 15-20 minutes. Then fry the patties on nonstick pan with 1 tbsp of olive oil on both sides (until they are white, which is about 2-3 minutes on each side). Toast the bun.

For the sauce: finely chop all ingredients and mix with yogurt and mustard

Build the burger: bun, sauce, tuna patty, lattuce, parsley, sauce and bun.